MANGE

                                                               Demodex canis

                                                               Introduction
 Demodex canis is the common mite species causing demodicosis in dogs, is acquired by pups from their dams within the first days of life. As normal skin inhabitants, the mites reside in hair follicles without causing cutaneous changes in most dogs. Commonly young dogs develop localized demodicosis, defined by convention as five or fewer lesions. These are nonpruritic, alopecic lesions that often develop on the face or limbs, although other areas may be involved.

                                                   Morphology 

The general structure of Demodex consists of the head, or gnathosoma, with its mouthparts, the trunk (idiosoma) and the extremities. The idiosoma includes the podosoma, into which the legs are attached, and opistosoma, distal to the legs. The elongated, cigar-like idiosoma, the ring-like segmentation of opisthosoma and very short legs with claw-like hooks at the tips are characteristic Demodex features. The gnathosoma is trapezoid and wider than its length. The slit-like genital pore of the female is located ventrally at the level of the fourth pair of legs, extending slightly caudal past it. The male genital, or aedeagus, is located dorsally in the genital pore that is at the level of the second pair of legs. The width of female D. canis is about 40 μm and the length varies between 165 μm and 285 μm. Males are shorter (150–210 μm) with a shorter and sharper opisthosoma that that of females. D. injai is longer then D.canis (330–370 μm) and D. cornei is shorter (90–140 μm). Molecular biological studies have indicated that D. cornei may not be an independent species, but rather a morphological variant of D. canis. The egg is spindle-shaped and sized 80–105 μm × 32–54 μm.

Morphology

• 0.25 mm
• Female longer, elongate
• Cylindrical
• Body divided into head, thorax, and abdomen

Head

• Has three jointed pedipalp
• One pair chelicerae
• Single hypostome

Thorax

• Ventral side with four pairs of stumpy legs
• Each leg is three jointed, vulva in female on ventral side
• On the dorsal side in males there is a longitudinal slit which is the genital opening

Abdomen

• Transversely striated

                                             Effects on host

• Injury to host occurs when mites puncture with their stylet like chelicerae the epithelial cells lining the hair follicles and glands to feed on the cell contents
• The host response in most cases leads to thrombosis of internal infestations
• Pustules initially seen on abdomen, neck, legs, also feet, face and thigh regions
• Dogs have repulsive mousy odour / rancid odour
• Itching is less
• In dogs both forms are seen
• Clinical signs evident in dogs less than 1 year old- presumably immuno deficient
• 1^st appear as mildly erythematous patch above eyes and corners of mouth, associated typically with hair loss- then spreads to forelegs, trunk
• Most resolve without treatment
• Death occurs in severely infected animals
• In generally predisposed or immuno depressed animals and in case of secondary infection, it develops into chronically severe, moist, purulent dermatitis - "Pustular Demodicosis” - unpleasant odour - rancid/mousy
• If generalized, there is intense redness, tenderness of skin which easily bleeds-Death occurs  in heavily infested animals
• Mild and moderate hypertrophy of the affected epithelia
• In some cases marked hypertrophy and cell destruction occurs
• Opening of hair follicle and ducts of glands are blocked
• Dermal papule formation and nodules
• Hair loss-secondary bacterial infection-inflammation, pruritus and pustule formation (Staphylococcus)
• Lesions occur on face and head and then spread-if untreated, death due to emaciation and toxaemia occurs

                                                                  Clinical signs

There are two major forms of demodecosis
1- Scaly demodicosis
2- Papulonodular demodicosis

                                                     
                                                      Scaly demodicosis

• Most common form.
• Dry, scaly dermatitis
• Itching, thickening and wrinkling of skin
• Loss of hair, reddening of skin
• Sec infection-rupture of follicular cells, inflammation, purulent exudates
• Localized or Generalized
• Repulsive mousy odour
• Red skin-bluish green- coppery reddish colour
• Skin is tender, easily bleeds
                   
      
                                 Papulonodular demodicosis
  
  

  • Obstruction of hair follicles, gland ducts
  • Leads to palpable cyst like/nodular swellings in the skin - traps mites within. Common form in Cattle, Goats & Pigs
  • Lesions enlarge as the mites multiply along with cellular debris and glandular secretions
  • Eventually rupture -leads to secondary infections and abscesses
  • Can rupture internally- introduce mites into lymphatics.
     Video- https://youtu.be/a0w4zUfyxw0

demodex canis

Demodex canis in dog

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